The present invention relates to photo controls, which are devices that are used, for example, to turn roadway lighting, signage and area lighting on and off.
Photo controls typically use electromechanical relays to switch the electric current to luminaires on and off. The power to a luminaire can be up to 1,000 watts, and the associated current can stress a relay's electrical contacts. For example, high currents cause the relay's contacts to pit and degrade, and eventually to stick together or, more precisely, to weld together. Thus, stress on the relay within a photo control is often an important limitation on the potential useful life span of a photo control.
In addition, due to the increased interest in saving energy and reducing light pollution, photo controls may cycle on and off more often, for example, turning on a luminaire at sunset, but then off again just after midnight when activity and traffic is greatly reduced, then back on just before dawn as activity starts to pick up, and then back off yet again at sunrise. This cycle effectively doubles the number of times the luminaire's relay must open and close.
Newer outdoor luminaires use LED's as the light source. LED's typically require an electronic driver. These electronic drivers may cause a high in-rush current, which further stresses the contacts of the photo control's relay.
Furthermore, because LED luminaires operate at lower temperatures, they have a longer life span than lighting system that operate at elevated temperatures, making it all the more imperative that the photo control for an LED-based luminaire have as long a lifespan as possible, ideally lasting as long as the LEDs in the luminaire itself.
One solution is to make the relay for a photo control larger, thus enabling the photo control to handle stress and thereby expand the relay's life expectancy. However, larger relays are more expensive. In addition, the size of the relay that can be used is constrained by the size of the photo control, which is in turn limited by industry standards.
Thus, there remains a need for a way to extend the lifespan of a relay in a photo-control for a luminaire.